Joining an NT Domain with Samba 2.0

Jeremy Allison, Samba Team

7th October 1999

Table of Contents

Joining an NT Domain with Samba 2.0

-----------------------------------

In order for a Samba-2 server to join an NT domain, you must first add
the NetBIOS name of the Samba server to the NT domain on the PDC using
Server Manager for Domains. This creates the machine account in the
domain (PDC) SAM. Note that you should add the Samba server as a "Windows
NT Workstation or Server", NOT as a Primary or backup domain controller.

Assume you have a Samba-2 server with a NetBIOS name of SERV1 and are
joining an NT domain called DOM, which has a PDC with a NetBIOS name
of DOMPDC and two backup domain controllers with NetBIOS names DOMBDC1
and DOMBDC2.

In order to join the domain, first stop all Samba daemons and run the
command

smbpasswd -j DOM -r DOMPDC

as we are joining the domain DOM and the PDC for that domain (the only
machine that has write access to the domain SAM database) is DOMPDC. If this is
successful you will see the message:

This command goes through the machine account password change
protocol, then writes the new (random) machine account password for
this Samba server into a file in the same directory in which an
smbpasswd file would be stored - normally :

/usr/local/samba/private

The filename looks like this:

<NT DOMAIN NAME>.<Samba Server Name>.mac

The .mac suffix stands for machine account password file. So in
our example above, the file would be called:

DOM.SERV1.mac

This file is created and owned by root and is not readable by any
other user. It is the key to the domain-level security for your
system, and should be treated as carefully as a shadow password file.

Now, before restarting the Samba daemons you must edit your
smb.conf file to tell Samba it should now
use domain security.

These are the primary and backup domain controllers Samba will attempt
to contact in order to authenticate users. Samba will try to contact
each of these servers in order, so you may want to rearrange this list
in order to spread out the authentication load among domain
controllers.

Alternatively, if you want smbd to automatically determine the
list of Domain controllers to use for authentication, you may set this line to be :

password server = *

This method, which is new in Samba 2.0.6 and above, allows Samba
to use exactly the same mechanism that NT does. This method either broadcasts or
uses a WINS database in order to find domain controllers to
authenticate against.

Finally, restart your Samba daemons and get ready for clients to begin
using domain security!

Why is this better than security = server?

------------------------------------------

Currently, domain security in Samba doesn't free you from having to
create local Unix users to represent the users attaching to your
server. This means that if domain user DOM\fred attaches to your
domain security Samba server, there needs to be a local Unix user fred
to represent that user in the Unix filesystem. This is very similar to
the older Samba security mode "security=server", where Samba would pass
through the authentication request to a Windows NT server in the same
way as a Windows 95 or Windows 98 server would.

The advantage to domain-level security is that the authentication in
domain-level security is passed down the authenticated RPC channel in
exactly the same way that an NT server would do it. This means Samba
servers now participate in domain trust relationships in exactly the
same way NT servers do (i.e., you can add Samba servers into a
resource domain and have the authentication passed on from a resource
domain PDC to an account domain PDC.

In addition, with "security=server" every Samba daemon on a
server has to keep a connection open to the authenticating server for
as long as that daemon lasts. This can drain the connection resources
on a Microsoft NT server and cause it to run out of available
connections. With "security =domain", however, the Samba
daemons connect to the PDC/BDC only for as long as is necessary to
authenticate the user, and then drop the connection, thus conserving
PDC connection resources.

And finally, acting in the same manner as an NT server authenticating
to a PDC means that as part of the authentication reply, the Samba
server gets the user identification information such as the user SID,
the list of NT groups the user belongs to, etc. All this information
will allow Samba to be extended in the future into a mode the
developers currently call appliance mode. In this mode, no local Unix
users will be necessary, and Samba will generate Unix uids and gids
from the information passed back from the PDC when a user is
authenticated, making a Samba server truly plug and play in an NT
domain environment. Watch for this code soon.